Various physical devices and systems have been developed for repelling fish and other aquatic animals or barring their passage, especially at the water intakes of industrial plants and electric generating stations to prevent the unnecessary killing of the fish and possible harm to the plant facilities, and the resultant expense of correcting the same. It is also desirable in other applications to attract fish to certain areas such as in the commercial fishing industry, to assist the fish in migration such as salmon moving upstream or downstream, and the like by guiding them to safe passage areas. Some of these prior devices, systems and methods use sound as the main stimuli for achieving the attraction or repulsion of the fish or other aquatic animals. Research has shown that certain sounds have certain effects on various species of fish or other aquatic animals and will either attract or repel the animals depending upon the particular sound applied into the water.
One example of such prior art is shown in Pat. No. 2,977,705, which shows one type of fishing lure used to attract a certain species of fish. In addition to the fishing lure of this patent, there are a considerable number of other fishing lures and related devices which uses various sounds in an attempt to attract fish to the lure.
U.S. Pat. No. 3,317,889 discloses an electronic device for producing a certain vibration in the water to repel dangerous fish such as sharks. It has been found that frequencies between 100 and 14,000 Hertz produce a sound that have a tendency to repel sharks from a certain area.
Pat. No. 3,414,873 discloses another type of system for producing acoustic signals which are transmitted into the water having certain frequency ranges and harmonic content which have been found to attract fish to the signal being produced by a sound generator.
U.S. Pat. No. 3,524,276 discloses another acoustic method in which sound projectors are placed in the water for producing acoustic stimuli within a frequency range of approximately 2.0to 3.2kilocycles, which have been found to cause jelly fish to rise to the surface of the body of water for subsequent collection.
U.S. Pat. No. 3,802,109 discloses another system for attracting fish to certain areas by producing sounds under the water in a predetermined timed sequence so as to effectively herd the fish into the desired area by the sound sequence in the water.
U.S. Pat. No. 3,859,954 discloses another type of apparatus for producing sonic vibrations in the water to repel sea life, referred to as a "steam hammer".
U.S. Pat. No. 4,646,276 discloses another underwater device for controlling fish in which vibrations are generated underwater within a watertight tank having certain fundamental frequencies together with means for periodically changing these frequencies. This patent furthermore includes a detailed description of other prior art devices and studies which have been conducted on the effect of the use of acoustic stimuli for controlling the behavior of fish.
The prior art assumes that the target animal will respond to the created sound without actual knowledge of the sound characteristics to which the animal is most sensitive. Some of the prior art methods rely on laboratory results of fish hearing experiments in which fish species hearing abilities encompass a 10,000 Hertz frequency range. Time consuming, costly trial and error testing is required to determine the most effective frequency.
Although many of these prior art devices, systems and methods may perform satisfactorily for certain types of fish and aquatic animals, none of these prior art systems have used or suggest using the sound produced by an aquatic animal inhabiting the specific underwater area in which the guidance is desired as a means for determining the particular acoustic stimuli for controlling the movement of the particular species of fish, whether it be to attract the fish or other aquatic animal to a certain area or to repel the fish or other aquatic animal from a certain area.
Therefore the need exists for an aquatic animal guidance system which will minimize harm to the animals by effectively repelling them from dangerous areas near human activities or effectively guiding them to a safe or desired areas with a minimum amount of time, equipment and expense. There is no such known prior art system or method which achieves these objectives.